As long as you have an active Cinema membership you will indeed be able to watch the Oscars live.
Ah right I get you now!
If I’m not mistaken it won’t start until 12 midnight on Monday. So I would suspect the membership will expire when you get to watch it I’m afraid.
No doubt if you go to “cancel” you’ll get a half decent offer which you could take for a month so you definitely are able to watch the Oscars.
If you cancelled your Cinema Membership and it says you can watch up until the 26th of April, then it depends at what time during the day you started the Cinema Membership the months previously prior to cancelling it.
I doubt very much your Cinema Membership will finish just before Midnight at the end of 26th of April 2021 (unless you started the Cinema Membership at around this time previously when you started it).